【文章內容簡介】 oretic background, and (3) extensive discussion of security and implementation considerations so that a solution provider can choose appropriate security requirements for itself. Γ В ? Memorized secrets are an important factor in human authentication. ? will specify publickey cryptographic techniques specifically designed to securely perform passwordbased authentication and key exchange. These techniques provide a way to authenticate people and distribute highquality cryptographic keys for people, while preventing offline bruteforce attacks associated with passwords. ? Rather, the purpose is to provide: (1) a reference for specification of a variety of techniques from which applications may select, (2) the appropriate theoretic background, and (3) extensive discussion of security and implementation considerations so that a solution provider can choose appropriate security requirements. Γ В ? IEEE will specify IdentityBased Cryptographic techniques based on Pairings. These offer advantages over classic public key techniques specified in IEEE 1363. Examples are the lack of a requirement to exchange or look up public keys of a recipient and the simplified use of shortlived keys. ? It is not the purpose of this project to mandate any particular set of identitybased publickey techniques, or particular attributes of publickey techniques such as key sizes. Rather, the purpose is to provide a reference for specifications of a variety of techniques from which applications may select. Γ В Certi ? Certi Corp. is a cryptography pany founded in 1985 by Gordon Agnew. ? The Certi intellectual property portfolio includes over 350 patents and patents pending worldwide that cover key aspects of elliptic curve cryptography (ECC): software optimizations, efficient hardware implementations, methods to enhance the security, and various cryptographic protocols. ? The National Security Agency (NSA) has licensed 26 of Certi39。s ECC patents as a way of clearing the way for the implementation of elliptic curves to protect US and allied government information. ? whuecc Γ В Latticebased Γ В 秘密 (密鑰 )分割 ? 秘密分割（多人共同持有秘密） 0. 秘密 K需要 t個人聯(lián)合打開 1. 產(chǎn)生隨機數(shù) R R … 、 Rt Rt=K⊕ R1⊕ R2… ⊕ Rt1 2. t個人分別持有 Ri 3. 恢復秘密 K＝ R1⊕ R2… ⊕ Rt1⊕ Rt Γ В 秘密的門限共享 ? (m， n)門限方案 – 秘密的恢復需要 n個人中的 m個參與即可 ? Lagrange插值方案 – 以 (3， n)門限方案為例 : 取多項式 f(x)=ax2+bx+K， a、 b是隨機數(shù)， K是秘密對于成員 i＝ 1…n ，給予 f(xi)=axi2+bxi+K，一般取 xi＝ i恢復秘密時只需 n中的三個 (x、 y)點即重構 f(x) Γ В 門限密碼學 (Threshold Cryptography) ? 一組人用門限方法共同持有一個私鑰，要對某個消息簽名 : (1) 可以恢復私鑰，然后簽名。這樣私鑰就公開暴露在組人面前，以后就不能用了。 (2) 不恢復私鑰而簽名。這樣私鑰可以繼續(xù)使用。 Γ В 時間戳服務 ? 在很多情況中，人們需要證明某個文件在某個時期存在。版權或專利爭端即是誰有產(chǎn)生爭議的工作的最早的副本，誰就將贏得官司。對于紙上的文件，公證人可以對文件簽名，律師可以保護副本。如果產(chǎn)生了爭端，公證人或律師可以證明某封信產(chǎn)生于某個時間。 在數(shù)字世界中，事情要復雜得多。沒有辦法檢查竄改簽名的數(shù)字文件。他們可以無止境地復制和修改而無人發(fā)現(xiàn)。在計算機文件上改變日期標記是輕而易舉的事，沒有人在看到數(shù)字文件后說：“是的，這個文件是在 1952年 12月 4日以前創(chuàng)建的?！? Applied Cryptography, Second Edition ? 權威機構： CA、公證處 Γ В Γ В in PGP fmt Γ В 實驗：時間戳服務 Γ В 盲簽名 Blind Signature ? A持有消息 m， B持有私鑰 d，計算 s ≡ md mod n，但是不泄露各自的輸入。 ? A讓 B簽署經(jīng)隨機盲化掩飾后的消息 m’≡ m*re mod n ? B計算 s’≡ m’d mod n ? A從而仍可得到 B對 m的簽名 s ≡ s’* reverse(r) ≡ (m*re)d*r 1 ≡ md*red1 ≡ md mod n Γ В 信息隱藏學 /隱寫術 Steganography ? 演示軟件 Dstego ? Google(―Dstego‖) – 能把秘密藏到聲音、圖像，甚至可執(zhí)行文件中 ? 閾下信道 Subliminal chann